Merge pull request phaserjs#3907 from iamchristopher/feature-data-manager-changedata-prev-val

Emit previous value with DataManager's `changedata` event

Author: photonstorm

src/data/DataManager.js

@@ -318,10 +318,11 @@ var DataManager = new Class({
                 {
                     if (!_this._frozen)
                     {
+                        var previousValue = list[key];
                         list[key] = value;
 
-                        events.emit('changedata', parent, key, value);
-                        events.emit('changedata_' + key, parent, value);
+                        events.emit('changedata', parent, key, value, previousValue);
+                        events.emit('changedata_' + key, parent, value, previousValue);
                     }
                 }